Characterisation of milk-clotting properties of Australian cardoon (Cynara cardunculus L) extracts and comparison with commercial coagulants on different substrates

Milk clotting properties of crude and partially purified extracts from flowers of Australian cardoon (Cynara cardunculus L.) were determined in full fat and skim milk obtained from ovine and bovine sources using a gelograph instrument. Properties including rennet clotting time (RCT), curd firming rate (CFR) and curd firmness were measured. Results showed that extracts from fresh flowers had better properties than those from dry flowers and partial purification with ammonium sulphate improved clotting ability of the water extract but not the citric acid extract. The milk clotting properties of partially purified water extract from fresh flowers were also compared to those of chymosin and commercially available microbial coagulant. With similar clotting times in all coagulant preparations, cardoon extract gave higher CFR than either chymosin or microbial coagulant in both bovine and ovine milk under the conditions of this study. However, the curd firmness was in the order of chymosin=cardoon > microbial coagulant in both milk systems. Ovine milk had shorter RCT, higher CFR and formed firmer curds than bovine milk irrespective of the extract or coagulant used, while the presence of fat lengthened the RCT and reduced the CFR and curd firmness.